Isotope Production in Fusion Systems
Fusion systems producing isotopes via neutron-driven transmutation can achieve economic viability well before reaching energy breakeven. Incorporating carefully selected feedstock materials in a blanket allows fusion systems to generate both electrical power and high-value isotopes, expanding the space of viable concepts, significantly enhancing the economic value of fusion energy, and supporting an accelerated path to adoption. We calculate the value of this co-generation and derive a new economic breakeven condition based on net present value. At lower plasma gain, $Q_{\mathrm{plas}}\lesssim 1$, high-value transmutation, such as medical radioisotopes, enables pure transmuter fusion systems operating at only watts to megawatts of fusion power: for example, a 3 megawatt system transmuting ${}^{102}\mathrm{Ru}\rightarrow{}^{99}\mathrm{Mo}$ could fulfill global ${}^{99}\mathrm{Mo}$ demand with $Q_{\mathrm{plas}} \ll 1$. At higher gain $Q_{\mathrm{plas}}\gtrsim 3$, it becomes viable to generate electricity in addition to isotopes. For example, co-production of electricity and gold, transmuted from mercury in a fusion blanket, can reduce the required plasma gain for economic viability from $Q_{\mathrm{plas}}\sim 10$-$100$ to $Q_{\mathrm{plas}}\sim 3$-$5$. We further highlight techniques to enhance transmutation with asymmetric neutron wall loading. Fusion neutron-driven transmutation therefore offers a revenue-positive pathway for deploying fusion energy at terawatt-scale, starting from smaller watt-to-megawatt-scale machines for radioisotope production and then scaling up to co-producing electricity and gold in larger fusion power plants.